Liu Yong, Chen Hongda, Wang Xiaoming
State Key Laboratory of Organometallic Chemistry and Shanghai Hongkong Joint Laboratory in Chemical Synthesis, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China.
School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China.
J Am Chem Soc. 2024 Oct 16;146(41):28427-28436. doi: 10.1021/jacs.4c09983. Epub 2024 Oct 2.
Understanding the nature of a transition-metal-catalyzed process, including catalyst evolution and the real active species, is rather challenging yet of great importance for the rational design and development of novel catalysts, and this is even more difficult for a bimetallic catalytic system. Pd(0)/carboxylic acid combined system-catalyzed allylic alkylation reaction of alkynes has been used as an atom-economical protocol for the synthesis of allylic products. However, the asymmetric version of this reaction is still rather limited, and the in-depth understanding of the nature of active Pd species is still elusive. Herein we report an enantioselective coupling between readily available aldimine esters and alkynes using a synergistic Cu/Pd catalyst system, affording a diverse set of α-quaternary allyl amino ester derivatives in good yields with excellent enantioselectivities. Mechanistic studies indicated that it is most likely a synergistic asymmetric molecular Cu catalysis with Pd nanoparticle catalysis. The Pd catalyst precursor is transformed to soluble Pd nanoparticles , which are responsible for activating the alkyne to an electrophilic allylic Pd intermediate, while the chiral Cu complex of the aldimine ester enolate provides chiral induction and works in synergy with the Pd nanoparticles.
理解过渡金属催化过程的本质，包括催化剂的演变和真正的活性物种，颇具挑战性，但对于新型催化剂的合理设计与开发却至关重要，而对于双金属催化体系而言，这更是难上加难。钯（0）/羧酸组合体系催化的炔烃烯丙基烷基化反应已被用作合成烯丙基产物的原子经济方法。然而，该反应的不对称版本仍然相当有限，对活性钯物种本质的深入理解仍然难以捉摸。在此，我们报道了一种使用协同铜/钯催化剂体系实现的、易于获得的醛亚胺酯与炔烃之间的对映选择性偶联反应，以良好的产率和优异的对映选择性得到了多种α-季碳烯丙基氨基酯衍生物。机理研究表明，这很可能是一种协同不对称分子铜催化与钯纳米颗粒催化。钯催化剂前体转化为可溶性钯纳米颗粒，其负责将炔烃活化成亲电烯丙基钯中间体，而醛亚胺酯烯醇盐的手性铜配合物提供手性诱导并与钯纳米颗粒协同作用。
